In the construction industry, the need for manipulating soil and other bases for construction is frequently encountered. This need typically occurs in the construction of buildings, paved roads and parking lots and other improvements. Oftentimes, the soil to be prepared is in a packed condition that is difficult to loosen or level. Therefore, mechanical scrapers of different designs have been developed to scrape, level or otherwise prepare earth for construction.
Such use requires that scrapers remove and transport large amounts of earth. Scrapers are typically wheeled and may be towed or self-propelled. Either type of scraper includes a pan which may be lowered to be brought into contact with the earth or raised to be brought out of contact with the ground. The scraper pan contains a bin or receptacle for the holding of earth. The pan may feature an opening located proximate the ground surface which may be selectively opened and closed with a scraper blade incorporated into the pan near the opening. When the pan is lowered and the opening opened, the blade scrapes earth into the bin of the pan as the scraper is moved along the surface. Other types of scrapers are permanently in the “open” position such that the blade contacts the earth upon lowering.
A common scraper used in road construction is mounted or hitched upon a large grader-type piece of equipment. A second configuration uses either a direct mount or a hitch mount scraper blade behind a towing tractor. Another type of scraper is the self-loading type in which the scraper includes a tractor portion which pulls the rear scraper portion.
Scrapers are typically used to remove earth at a work site and transport the earth over a substantial distance to another site where earth is needed or to a dump site where excess earth can be accepted. Generally, a haul road from the work site to the intended dump site is planned for use by all earth moving vehicles such that the rest of the construction area is minimally disturbed. Because of the tremendous amount of weight carried by loaded earth moving vehicles, the haul road undergoes extreme compression. Frequently, any soft patch of earth is more greatly compressed than any neighboring hard-packed earth. Such differences in compression cause ruts which impact the wheels of the earth moving vehicles during transport. The wheels transfer the impact force to the vehicles and cause the vehicles to experience bounce, in which the weight of the vehicles is transferred up and down as the vehicles move along the haul road.
The bounce of the vehicles, in turn, pumps the road beyond the initial rut and causes further rutting until virtually the entire road is rutted from the work site to the dump site. For instance, an initial rut causes a vehicle to bounce and pump the haul road beyond the rut. Such rutting typically requires earth moving vehicles to travel at lower speeds than is preferred which causes a substantial increase in the amount of time needed to complete an earth moving operation.
This problem may be encountered even when traveling on a smooth roadway without variable initial earth compaction because the vibration inherent in the use of motorized vehicles is often translated into a bouncing motion by the scraper's wheels. When dealing with very heavy equipment and loads, such small vibration quickly leads to a large bouncing force which is able to pump the roadway and cause rutting.
Another problem is frequently encountered by scrapers which are used on hill sides or other uneven terrain. Often scrapers employed in such use slide down the hillside or even roll over during operation. Sliding is typically caused by the heavy load of the scraper coupled with the poorer traction of the scraper's wheels compared to the towing device's wheels or the tractor portion's wheels. Rolling over usually occurs when the uphill wheel of the scraper encounters a bump or rut which causes the uphill tire to bounce. The upward shift in weight causes the center of gravity to shift upward and results in the scraper rolling over, especially when the scraper is holding a large amount of weight.
Another problem faced by scrapers is the uniform compaction of earth under the scraper wheels in the direction of travel. Use of scrapers along a path often results in grooves in which the scraper's wheels ride. Eventually such grooves become so deep that the underside of the scraper hits the earth between the grooves and the scraper becomes stuck. This problem is aggravated when working in wet areas where a loaded scraper may sink into the earth on its first pass across a path. Often a fully loaded scraper must be unloaded before it can be removed from its stuck position, resulting in a large delay in completing the job. Therefore, the resistance to sinking into soil, or flotation, would be highly desirable for a scraper.
As can be seen, regardless of the type of scraper utilized, several problems are encountered when removing and transporting large amounts of earth. Therefore, in view of these problems and their consequences, there is a need in the field of earth scraping for an improved scraper.